In a Time view chart, a trailing window is a rolling window of time prior to each point used to calculate that point.
It is common to set the trailing window equal to the time resolution between two points (for example, resolution 1 day, trailing 1 day). With this setting, every data point uses data that does not appear in other data points.
Less commonly, you might want to smooth the data by setting a trailing window that is longer than the time resolution between the data points.
You can set a trailing window for an actor property in addition to setting one in the top-level query. If the trailing window for an actor property differs from that specified for the top-level query, the actor property trailing window applies for the calculation of the actor property value.
See Specify Relative Time in a Query in the User Guide.